Tolerance of soybean varieties to white mold

As many of you know, the Iowa Soybean Promotion Board supports testing by the ISU Department of Plant Pathology of varieties tolerant to soybean white mold. Following preliminary experiments in 1995, we tested 63 entries from private and public sectors in the 1996 growing season.

Although results have been presented on various occasions, we continue to receive numerous requests from soybean producers for this information. Here is a portion of the data. Full results can be found on our World Wide Web site at this address: http://www.exnet.iastate.edu/Pages/plantpath/whitemold.html

The experiments were conducted at three locations and results at the following locations are presented: the Humboldt research plot in Humboldt County and the ISU Kanawha Research Farm in Hancock County. The Humboldt field has been naturally infested with soybean white mold for years and has the highest disease pressure among all testing sites. The Kanawha field was uniformly infested with a high sclerotia density in the fall of 1994 and again in the fall of 1995 using infested soybean debris. We also inoculated the plants with white mold culture at flowering time. Data of control plots showed that inoculation at flowering time was not effective and infections were from spores produced by sclerotia in the soil.

Table 1 and Table 2 (below) list the varieties whose tolerance was ranked in the top 30 at each location. Two susceptible varieties, A2242 and Williams 82, were grown as checks, and their results also are provided.

Tolerance of each variety was measured as the percentage of plants killed. The fewer plants killed for a variety, the higher the tolerance and the higher the variety's rank. The number of plants killed differed between locations because of varying disease pressure. The Humboldt site had higher disease pressure than the Kanawha site. For all data presented, there were four replications of each entry at each location. Maturity information is provided by individual companies or from 1995 ISU uniform yield tests.

To select a variety, compare the percentage of dead plants with that of the most susceptible varieties and look for consistency in tolerance rankings. Also, select varieties with higher yields. Keep in mind that these two locations had high disease pressure, which may not be present in your fields. In fields with mild disease pressure, varieties that did not receive high ranks in these two fields may do well.

Table 1. White mold resistance at the Humboldt plot

Company

Variety

Tolerance rank

Plants killed (%)

Yield estimate (bu/a)

Maturity

Corsoy79

1

8.0

54.0

2.1

Dassel

2

9.3

48.9

1.1

Asgrow Seed Company

A 2506

3

10.0

44.9

2.5

Custom Farm Seed

CFS 181

4

10.0

49.8

1.8

Hy-Vigor Seeds

1150

5

11.3

55.6

1.5

Sands of Iowa, Inc.

SOI 260

6

12.5

54.8

2.0

Mark Seed Company

MRK 9519

7

13.0

59.4

2.0

Pioneer Hi-Bred Int'l, Inc.

9163

8

13.8

52.1

1.6

Midwest Seed Genetics, Inc.

G 1885

9

14.3

56.5

1.9

Stine Seed Company

01526-84

10

16.3

58.7

-

Terra International, Inc.

TS194

11

17.5

53.6

1.9

Northrup King Company

S19-90

12

17.5

47.2

1.9

Kruger Seed Company

K1990

13

18.8

58.5

1.9

AgriPro Seeds, Inc.

AP 1876

14

18.8

52.7

1.8

Asgrow Seed Company

A 1900

15

20.0

48.2

1.9

Gutwein and Sons, Inc.

7200

16

20.0

45.0

2.0

Parker

17

23.8

55.3

1.4

AgriPro Seeds, Inc.

AP 1995

18

25.0

53.1

1.9

DeKalb Plant Genetics Company

CX173

19

26.3

46.3

1.7

BSR101

20

27.5

39.9

1.9

Merschman Seeds

ex01018-E

21

30.0

39.2

-

Latham Seed Company

Latham 440

22

31.3

44.5

2.1

Dairyland Seed Company

DSR-220STS

23

32.5

42.1

2.2

Sieben Hybrids, Inc.

SS 273

24

32.5

38.4

2.7

Kenwood

25

33.8

43.0

2.1

Story Brand Seeds

ST 203

26

35.0

42.0

1.9

Sands of Iowa, Inc.

SOI 242

27

36.3

37.3

2.2

Custom Farm Seed

CFS196

28

37.5

43.4

1.9

Dairyland Seed Company

DSR-277

29

40.0

34.6

2.7

IA2007R

30

40.0

34.3

2.6

Asgrow Seed Company (Check)

A 2242

60

70.0

26.3

2.2

(Check)

Williams 82

62

78.8

14.1

-

Table 2. White mold resistance at the Kanawha plot

Company

Variety

Tolerance rank

Plants killed (%)

Yield (bu/ac)

Pioneer Hi-Bred Int'l, Inc.

9163

1

0.5

56.0

Dassel

2

1.6

34.0

Corsoy79

3

2.8

46.6

Northrup King Company

S19-90

4

2.8

50.0

Custom Farm Seed

CFS 181

5

3.4

52.3

Terra International, Inc.

TS194

6

4.5

43.9

Asgrow Seed Company

A 2506

7

6.1

50.0

Asgrow Seed Company

A 1900

8

6.8

48.9

Hy-Vigor Seeds

1150

9

7.1

48.3

Parker

10

7.4

52.0

Midwest Seed Genetics

G 1885

11

7.8

53.3

DeKalb Plant Genetics Company

CX173

12

10.4

47.6

AgriPro Seeds, Inc.

AP1876

13

13.1

41.5

Dairyland Seed Company

DSR-277

14

13.9

45.6

Mark Seed Company

MRK 9519

15

15.0

50.3

Gutwein & Sons, Inc.

7200

16

15.6

42.4

Latham Seed Company

720 Brand

17

15.8

47.8

Latham Seed Company

440 Brand

18

15.9

49.8

Sands of Iowa, Inc.

SOI 260

19

16.3

48.1

Stine Seed Company

01526-84

20

16.5

45.5

Kruger Seed Company

K1990

21

16.8

47.5

Mark Seed Company

MRK 9227

22

16.8

48.3

Sands of Iowa, Inc.

SOI 242

23

16.9

48.1

Stine Seed Company

1970

24

18.1

50.2

Marlin Wilkin and Sons

MWS261

25

18.3

44.1

BSR101

26

18.4

40.0

Custom Farm Seed

CFS196

27

18.6

45.0

Merschman Seeds

ex01018-E

28

19.1

45.7

Bell

29

19.9

41.5

Lynks Seeds

5269

30

20.6

47.6

(Check)

Williams82

59

53.8

23.2

Asgrow Seed Company (Check)

A 2242

61

64.0

30.1

This article originally appeared on pages 191-192 of the IC-476(26) -- December 16, 1996 issue.